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Enhanced utilization of wastewater nutrients Water management solutions need to be improved. New technologies in wastewater and sewage sludge treatment would enable more efficient nutrient recovery, allowing them to be utilised in food production and industry due to their greater degree of purity. This would also reduce negative environmental impacts. The recovery of nutrients would increase security of supply in an uncertain world situation, where the availability of nutrients can become even more difficult.
Recovered nitrogen 6 % Recovered phosphorus
92%
Recovered nitrogen 30 % Recovered phosphorus
CURRENT WASTEWATER TREATMENT
96%
Recovered nitrogen 73 % Recovered phosphorus
SHORT-TERM SOLUTIONS
96%
LONG-TERM SOLUTIONS
New technologies at wastewater treatment plants
Source separation
The new wastewater solutions in Finland enable significantly higher nitrogen recovery than at present. The amount of recovered phosphorus does not increase much, but the phosphorus is recovered in a more usable form for plants than at present. LEHTORANTA ET AL. 2022 8, SYKE 2022 9
Recommendations for cities and municipalities New technologies should be introduced in wastewater treatment plants and in sewage sludge processing, especially for nitrogen recovery. Nitrogen is a critical nutrient in food production and in industrial processes. In new residential areas, and when renewing old sewage networks, source separation of wastewater should be introduced whenever possible. Source separation can be imple-
mented with double drainage, where nutrient-rich wastewater, such as blackwater, is treated separately from other wastewater. The criteria for public procurement should include criteria that promote nutrient recovery and recycling. For example, in the procurement of sludge treatment it would be good to set a requirement for nitrogen recovery.
For legislators Clear obligations should be set for the recovery of nutrients in both EU and national legislation. More comprehensive limits values and monitoring requirements should be set for harmful substances in recycled nutrients, to ensure safe nutrient recycling.
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Improved nutrient recovery Improving the recovery of wastewater nutrients would enable production of essential raw materials for agriculture and industry. With new techniques, nitrogen recovery could be tripled in wastewater treatment plants and sludge treatment plants compared to the current situation. At the same time, phosphorus could be recovered in a more suitable form for agricultural use than at present.1 For example, in 2020, nearly 140,000 tons of artificial nitrogen was used in agriculture. In principle, 5–15 percent of this could be replaced with nitrogen recovered from municipal wastewater. Correspondingly, nearly 11,500 tons of artificial phosphorus was used, of which about 20 percent could be replaced with phosphorus recovered from wastewater.2 Industry uses nitrogen in many of its processes, for example in the removal of flue gases. The urea used in forest industry wastewater treatment could be partially replaced with nitrogen recovered from sludge treatment. Nitrogen recovery could be enhanced by recovering the nitrogen from reject water formed during sludge treatment. This would reduce the nitrogen load coming to the wastewater treatment plant, as well as the greenhouse gas emissions caused during nitrogen removal, as currently, reject water is usually returned to the wastewater treatment plant. Nearly 80 percent of sewage sludge goes to anaerobic digestion3. Anaerobic digestion should be increased in the future, as it enables the conversion of nitrogen into a usable form for plants and the recovery of the energy
EFFICIENT NUTRIENT RECYCLING Annual amount of nutrients produced in wastewater per person in Finland
PRESENT SYSTEM
GREYWATER AND BLACKWATER
NITROGEN 4.9 KG PHOSPHORUS 0.65 KG
WASTEWATER TREATMENT
USE OF PHOSPHORUS AND NITROGEN IN AGRICULTURE IN FINLAND
NITROGEN about 228,000 tons/year Artificial fertilizers 65% Manure 33% Recycled fertilizers (incl. sewage sludge) 2% PHOSPHORUS about 32,000 tons/year Artificial fertilizers 35% Manure 60% Recycled fertilizers (incl. sewage sludge) 5% MARTTINEN ET AL. 2017 7
contained in the sludge as biogas. In addition, anaerobic digestion reduces greenhouse gas emissions caused by sludge treatment. After the recovery of nutrients, the anaerobically digested sewage sludge should be processed with, for example, thermal methods instead of composting in order to reduce the occurrence of harmful substances. The current municipal wastewater treatment process has been developed to reduce pollution of waterways. The process is based on the removal of nutrients and organic matter, not on their recovery and utilisation. Current wastewater treatment methods cause greenhouse gas emissions. The emissions are mainly caused by the volatile nitrogen compounds of the denitrification process and the energy used in the process. Emissions are also caused by the production of chemicals used in the phosphorus precipitation.
Source separation of wastewater
A long-term objective in wastewater management should be source separation of wastewater. Source separation uses double drainage. Consequently, blackwater from households and nutrient-rich wastewater generated in some industries can be sewered separately from nutrient-poor SOURCE wastewater containing high concentrations of harmful substances, such SEPARATION as greywater from households and wastewater from landfills and indusDouble trial plants. This prevents nutrient-rich wastewater from being diluted drainage into nutrient-poor wastewater with a high water volume, from which nutrient recovery is more difficult. GREYBLACKThe processing of separated nutrient-rich wastewater enables effiWATER WATER cient and safe recycling of nutrients for use in agriculture and industry. In connection with processing, biogas can also be produced from sewage sludge. Source separation reduces the load on wastewater treatment NITROGEN NITROGEN 0.4 KG 4.5 KG plants and the treatment plants’ consumption of chemicals and energy. Source separation of urban residential wastewater would reduce PHOSPHORUS PHOSPHORUS 0.15 KG 0.5 KG greenhouse gas emissions from wastewater treatment in urban areas to about half of their present levels. The climate benefits would be even greater if the nutrients and energy recovered through source separation reduces the use of artificial fertilizers and fossil energy.2 WASTEWATER TREATMENT Solutions based on source separation of wastewater are already in use in some sparsely populated areas. Such solutions have been introduced in new urban residential areas in Sweden and the Netherlands, SEPARATE for example. The experiences have been good and the costs have been TREATMENT reasonable, and bigger systems are being planned. LEHTORANTA 2022 2
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The utilisation of nutrients in wastewater promotes security of supply and sustainability transformation
Accelerating the introduction of new technologies New techniques for recovering nutrients from wastewater have been developed in Finland and abroad. Some of the techniques are still under development. The high price of fertilizers and nutrient products improves the profitability of investments in the production of recycled nutrients. The Ministry of the Environment grants support for research and investments promoting the recovery of nutrients and the production of safe fertilizer products4. The aim of the support is to improve nutrient and energy self-sufficiency and to develop the recycled nutrient market. Research is still needed into matters such as how government can best promote solutions that support the achievement of security of supply and sustainability goals. Highly processed nutrient products are most likely to end up in industrial use. From the point of view of the security of food production, it would be important that, if necessary, enough nutrients are also steered to agricultural use. Forty percent of Finland’s sewer network will need renovation by 20405. This would require investments of more than EUR 200 million. In connection with renovations, it should be examined whether it would be appropriate to switch to source separation of wastewater. The introduction of new techniques at wastewater treatment and sludge processing plants should be accelerated by establishing criteria for the procurement of sewage sludge processing services. Criteria can be set for promoting nutrient recycling, utilisation of final products, energy efficiency, and reducing greenhouse gas emissions. Good experiences have been gained from circular economy criteria, for example, in the tenders for Porvoo’s water procurement, and Turku region’s sewage treatment plant’s sludge treatment service. New circular economy technologies have been introduced at the sludge incinerator in Rovaniemi.
Managing harmful substances Municipal wastewater treatment plants receive wastewater from different sources, and the wastewater contains a wide range of harmful substances. Current wastewater and sludge treatment processes have not been designed to remove compounds that are harmful to the environment. Fertilizer products produced from sludge have been shown to contain harmful substances6. Especially persistent compounds, such as PFAS compounds, can reach the soil environment through the use of sludgebased fertilizers. Harmful substances can accumulate from the soil to cultivated plants, soil organisms and further up the food chain. Long-term impacts and combined effects of harmful substances on the environment are poorly known. Information on the occurrence, behaviour, and effects of many compounds is incomplete. In addition, the abundance of various compounds makes risk assessment difficult. The new techniques of nutrient recovery and source separation of wastewater reduce the spread of harmful substances into the environment in fertilizers. The introduction of these solutions is a prerequisite for the safe utilisation of nutrients contained in wastewater, for example in agriculture. In order to increase the use of wastewater-based nutrients, their safety must be guaranteed. It is important that more comprehensive criteria are set for the occurrence of harmful substances in fertilizers and for their environmental monitoring, which take into account their intended use.
ONLY A SMALL PORTION OF NITROGEN FROM WASTEWATER IS CURRENTLY RECOVERED
In the current wastewater treatment process in Finland, on average, about a third of the nitrogen ends up in sludge left over in the process. About a third evaporates into the atmosphere primarily as harmless nitrogen gas, in addition to which a small amount of dinitrogen oxide, a very strong greenhouse gas, is formed. About a third of the nitrogen ends up in waterways. Depending on the further processing of the sludge, a variable proportion of the nitrogen returns via reject water back to the wastewater treatment plant. Calculation of the flow of nitrogen is based on the average wastewater treatment methods. INTO THE ATMOSPHERE 8,400 t/year POPULATION LANDFILLS INDUSTRY HOSPITALS
NITROGEN IN WASTEWATER TO TREATMENT PLANTS 28,000 TONS A YEAR
INTO WATERS 10,400 t/year
INTO SLUDGE 9,200 t/year LEHTORANTA ET AL. 20211, LEHTORANTA ET AL. 2022 8 , SYKE 2022 9 , VILPANEN & SEPPÄLÄ 20213
RECOVERED IN SLUDGE PROCESSING 3,100 t/year
FOR URBAN LANDSCAPING 800 t/year FOR AGRICULTURE 800 t/year FOR OTHER PURPOSES 150 t/year
REJECT WATER 6,100 t/year REJECT WATER 1,350 t/year
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The worthwhile recovery of wastewater nutrients Wastewater nutrients can replace artificial fertilizers used in agriculture and nutrients used in industry. This improves security of supply.
The infiltration of harmful substances into the food chain and environment is reduced.
Dependence on fossil fuels and imports is reduced. Natural resources are saved.
Source separation of wastewater reduces the formation of sewage sludge, which has low fertilizer value and is problematic due to harmful substances.
Renewal of EU directive The European Union is currently renewing its directive on the treatment of municipal wastewater. The proposed directive emphasises circular economy in the recovery of valuable materials. According to the proposal, minimum requirements should be set for the recovery of nutrients in sewage sludge treatment. Microplastics in the sludge, as well as harmful substances in non-domestic wastewater should also begin to be monitored. The directive should set clear and ambitious requirements for nutrient recovery. It should consider nutrients
Utilization of wastewater nutrients Authors: Suvi Lehtoranta, Vuokko Laukka, Päivi Fjäder, Lauri Äystö, Juha Grönroos, Petri Ekholm, Jyrki Laitinen, Helena Valve, Katriina Alhola, Sari Kauppi • Editor: Leena Rantajärvi • Layout: Ahoy Publisher: Finnish environment institute SYKE References 1 Lehtoranta, S., Malila, R., Äystö, L., Fjäder, P., Mustajoki, J. & Laukka, V. 2021. Jätevesien ravinteet kiertoon turvallisesti ja tehokkaasti (In Finnish with English abstract). Suomen ympäristökeskuksen raportteja 18/2021. 2 Lehtoranta, S. 2022. Towards circular economy in wastewater management – environmental impacts, benefits and drawbacks of improved nutrient recovery and recycling by source separation. 3 Vilpanen, M. & Seppälä, P. 2021. Yhdyskuntalietteen käsittelyn ja hyödyntämisen nykytilannekatsaus (In Finnish). Vesilaitosyhdistyksen monistesarja nro 71. Suomen Vesilaitosyhdistys ry. 4 Ympäristöministeriö. Rahoitusta tarjolla investoinneille sekä tutkimus-, kehittämis- ja innovaatiohankkeille yhdyskuntien jäte- ja sivuvirtojen ravinne- ja energiapotentiaalin hyödyntämiseksi (In Finnish). (ym.fi) 5 VVY 2020. Vesihuollon investointitarpeet vuoteen 2040 (In Finnish with English abstract). Vesilaitosyhdistyksen monistesarja nro 63. 6 Äystö. L., Högmander, P., Fjäder, P. & Salminen, J. 2022. Haitalliset aineet kierrätyslannoitteissa ja niiden raaka-aineissa (In Finnish with English abstract). Suomen ympäristökeskuksen raportteja 27/2022. 93 s. ISBN 978-952-11-5497-3.
from sewage sludge processing and those recovered directly from wastewater. It is important to monitor the implementation of the minimum requirements for nutrient recovery. The monitoring should also cover source-separated wastewater, which is not processed at municipal treatment plants. This requires a new kind of monitoring and reporting. European Commission 2022. Proposal for a revised Urban Wastewater Treatment Directive
Marttinen, S., Venelampi, O., Iho, A., Koikkalainen, K., Lehtonen, E., Luostarinen, S., Rasa, K., Sarvi, M., Tampio, E., Turtola, E., Ylivainio, K., Grönroos, J., Kauppila, J., Koskiaho, J., Valve, H., Laine-Ylijoki, J., Lantto, R., Oasmaa, A. & zu Castell-Rüdenhausen, M. 2017. Kohti ravinteiden kierrätyksen läpimurtoa (In Finnish). Luonnonvara- ja biotalouden tutkimus 45/2017. Luonnonvarakeskus, Helsinki. 8 Lehtoranta, S., Laukka, V., Vidal, B. Heiderscheidt, E., Postila, H., Nilivaara, R. & Herrmann, I. 2022. Circular economy in wastewater management – the potential of source-separating sanitation in rural and peri-urban areas of northern Finland and Sweden. Frontiers in Environmental Science 10, 804718. 9 SYKE 2022. Yhdyskuntien jätevesien kuormitus vesiin (In Finnish). (ymparisto.fi) Further information Ravinteiden kierrätyksen toimenpideohjelma 2019–2030 (In Finnish). Ympäristöministeriö 2019. Circular Economy Action Plan. For a cleaner and more competitive Europe. European Commission 2020. Ylivainio, K., Äystö, L., Fjäder, P., Suominen, K., Lehti, A., Perkola,N., Ranta, J., Meriläinen, P., Välttilä, V. & Turtola, E. 2020. Jätevesilietteen pitkäkestoinen fosforilannoitusvaikutus ja yhteys ympäristö- ja ruokaturvallisuuteen (In Finnish with English abstract). Luonnonvaraja biotalouden tutkimus 55/2020. 120 s. ISBN 978-952-380-018-2. 7
www.syke.fi/policybriefs/en ISBN 978-952-11-5536-9 (PDF) • ISBN 978-952-11-5537-6 (nid.)